Conventionally, a printing apparatus is known for forming an image with a decolorable image forming material, for example, toner.
A decoloring apparatus is used to decolor an image. The decoloring apparatus prints a mark indicating the decolored times on a medium.
The decoloring apparatus determines that a sheet reused for the certain times, for example, five times, is non-reusable later according to the mark. However, actually, the reusable times differs in different media. A thick sheet can be reused more than five times.
However, the decoloring apparatus records the same marks on the media regardless of the type of the media, and discharges a paper determined to be non-reusable as the paper has been used more than the uniform reuse times to a reject tray that accumulates the non-reusable paper.